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Otakar Bokůvka, Michal Jambor, Libor Trško, František Nový and Barbara Lisiecka
This paper presents three physical sources of the electric field in dielectrics: excess free volume charges with the distribution qv(x,y,z), free surface charges with the distribution qs(x,y,z) and frozen polarization state in the dielectric. They have a deciding influence on the parameters of the electret, in particular they determine the total lifetime of the electret and technical components made of it. The indeterminacy related to the mutual proportions of the spatial and surface charges was discussed: one can find an infinite number of distributions of surface qse(x,y,z) and spatial qve(x,y,z) charges leading to the same distribution of the electric field E(x,y,z). A general case of electret was considered, where a coexistence of relaxation decay of frozen polarization and Maxwellian relaxation dependent on volume conductivity of the dielectric is assumed. An attempt to interpret the charge lifetime in real electrets was made.
Yi Sun, Tao Xu, Yuanjie Shu and Fachun Zhong
HNS (2, 2′, 4, 4′, 6, 6′-hexanitrostillbene) is a heat-resistant photosensitive explosive widely used in the booster charge. Investigation of the photodecomposition mechanism may provide important information for controlling and enhancing the detonation performance, also for the lifetime prediction. The UV-induced photodecomposition of HNS has been subjected to experimental studies. The UV-Vis spectra, X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance spectra (EPR) demonstrate the formation of NO2 free radicals and nitroso derivatives of HNS upon UV irradiation, which proves well known facts that C-NO2 breaking and removal of oxygen from the nitro group take part in the photodecomposition of HNS.
Zr0.99Gd0.01O2, Zr0.98Gd0.01Dy0.01O2 and Zr0.98Gd0.01Yb0.1O2 phosphors were synthesized by Pechini method at 1200 °C for 12 h in air. The phosphors were characterized by using X-ray powder diffraction (XRD), differential thermal analysis/thermal gravimetry (DTA/TG), scanning electron microscopy (SEM) and photoluminescence spectrofluorometer (PL). X-ray powder diffraction studies showed that the phosphors were crystallized as monoclinic and tetragonal multiphases. The particle size of the phosphors after heat treatment at 1200 °C was found to be of 200 nm to 250 nm. Luminescence studies on these phosphors have been carried out on the emission and excitation, along with lifetime measurements. The results of emission analysis indicate that the phosphors are expected to find potential applications as new optical materials.
Qu Yuqiu, Zhang Liuyang, An Limin and Wei Hong
The effect of different organic charge transporting materials on the photoluminescence of CdSe/ZnS core/shell quantum dots has been studied by means of steady-state and time-resolved photoluminescence spectroscopy. With an increase in concentration of the organic charge transporting material in the quantum dots solutions, the photoluminescence intensity of CdSe/ZnS quantum dots was quenched greatly and the fluorescence lifetime was shortened gradually. The quenching efficiency of CdSe/ZnS core/shell quantum dots decreased with increasing the oxidation potential of organic charge transporting materials. Based on the analysis, two pathways in the photoluminescence quenching process have been defined: static quenching and dynamic quenching. The dynamic quenching is correlated with hole transporting from quantum dots to the charge transporting materials.
In the present study, ZrO2co-doped with Gd3+/Sm3+and Gd3+/Er3+ions have been synthesized using Pechini method. Phase composition, morphology and photoluminescence properties of the synthesized phosphors were investigated by using X-ray powder diffraction (XRD), differential thermal analysis/thermal gravimetry (DTA/TG), scanning electron microscopy (SEM) and photoluminescence spectrofluorometer (PL). After heating at 1200 °C, XRD revealed that the phosphors were crystallized as monoclinic and tetragonal multiphases. SEM images indicated that the phosphors consist of fine and spherical grains with a size around 200 nm to 250 nm. Luminescence studies of these phosphors have been carried out on the emission and excitation, along with lifetime measurements
Tran Hoang Quang Minh, Nguyen Huu Khanh Nhan, Nguyen Doan Quoc Anh, Tran Thanh Nam and Hsiao-Yi Lee
Based on some advantageous properties, such as fast response time, environment friendliness, small size, long lifetime, and high efficiency, white LEDs are increasingly used in common illumination applications. In this research, by co-doping of redemitting Sr2Si5N8:Eu2+ phosphor and adding SiO2 particles to yellow-emitting YAG:Ce phosphor compounds, a new approach for improving color uniformity and color rending index of remote-phosphor structure white LEDs is proposed and demonstrated. The obtained results clearly indicate that the color rendering index (CRI) and color uniformity (ΔCCT) significantly depend on Sr2Si5N8:Eu2+ concentration. The results provide a potential practical solution for manufacturing remote-phosphor white LEDs (RP-WLEDs) in the near future.
Traditionally, powder metallurgy has been based on two major industrial sectors – ferrous precision parts and hardmetals. Both of them relied heavily on the automotive industry, with focus on internal combustion engines. Today, there is an increasing trend towards alternative drivetrain systems, and powder metallurgy faces the challenge to find new applications to replace those lost with the decrease of classical internal combustion drives. In this presentation it is shown that the main strength of powder metallurgy lies in its enormous flexibility regarding materials, geometries, processing and properties. This enables PM to adapt itself to changing requirements in a changing industrial environment. Examples given are PM parts in alternative drivetrain systems, new alloying concepts and processing routes offering distinct advantages. With hardmetals, innovative microstructures as well as sophisticated coatings offer increased lifetime, applications ranging from metalworking to rockdrilling and concrete cutting. A particularly wide area is found in functional materials which range from components for high power switches to such for fuel cells. Soft and hard magnets are accessible by PM with particularly good properties, PM having in part exclusivity in that respect, such as for NdFeB superhard magnets as well as soft magnetic composites (SMCs). Metal injection moulding (MIM) is gaining further ground, e.g. in the medical area which is a fast-growing field, due to demographic effects. Finally, most additive manufacturing techniques are powder based, and here, the knowledge in powder handling and processing available in the PM community is essential for obtaining stable processes and reliable products. Conclusively it can be stated that PM is on the way to fully exploit its potential far beyond its traditional areas of applications.
Adam Szyszka, Michał Obłąk, Tomasz Szymański, Mateusz Wośko, Wojciech Dawidowski and Regina Paszkiewicz
lifetime. The conclusions of the tests were as follows: the largest lifetime had the tip with the conductive diamond coating (DDESP-FM/NANOSensors) but, due to relatively large radius of the tip, the images resolution and contrast were poor. The best images quality was obtained using Cr/Pt (MULTI75E-G/BudgetSensors) and Pt/Ir (SCM-PIT/NANOSensors) coated tips but the second one guaranteed better stability and longer usage. The gold covered AFM tip (PPP-NCSTAu/NANOSensors) had a very short lifetime due to very low hardness of this metal, while the images obtained using Co
Rafał Chodun, Katarzyna Nowakowska-Langier and Krzysztof Zdunek
comparison to uncoated tools, 4 fold increase of lifetime; by comparison to TiN coated tool synthesized in standard, current oscillating conditions, 3-fold increase of lifetime. Acknowledgements This work was supported by the National Science Centre within the Project No. 2013/09/B/ST8/02418. References  Sokolowski M., J. Cryst. Growth , 54 (1981), 519. 10.1016/0022-0248(81)90507-8 Sokolowski M J. Cryst. Growth 54 1981 519  Sokolowski M., Sokolowska S., J. Cryst. Growth , 57 (1982), 185. 10.1016/0022-0248(82)90265-2 Sokolowski M Sokolowska S